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Ch. 5 - Integration
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 5, Problem 5.2.77a

{Use of Tech} Midpoint Riemann sums with a calculator Consider the following definite integrals.
(a) Write the midpoint Riemann sum in sigma notation for an arbitrary value of n.


โˆซโ‚€โด (4๐“โ€• ๐“ยฒ) d๐“

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Step 1: Understand the problem. A midpoint Riemann sum is a method to approximate the value of a definite integral by dividing the interval into subintervals, calculating the function value at the midpoint of each subinterval, and summing the areas of the rectangles formed. The goal is to express this sum in sigma notation for an arbitrary number of subintervals, n.
Step 2: Define the interval and subintervals. The integral โˆซโ‚€โด (4๐“ - ๐“ยฒ) d๐“ is over the interval [0, 4]. Divide this interval into n subintervals of equal width, ฮ”๐“ = (4 - 0)/n = 4/n.
Step 3: Determine the midpoints of the subintervals. The midpoints of the subintervals are given by ๐“แตข = a + (i - 0.5)ฮ”๐“, where a = 0 is the starting point of the interval, i is the index of the subinterval (ranging from 1 to n), and ฮ”๐“ = 4/n.
Step 4: Write the function value at the midpoints. For each midpoint ๐“แตข, evaluate the function f(๐“) = 4๐“ - ๐“ยฒ. Substitute ๐“แตข into the function to get f(๐“แตข) = 4(0 + (i - 0.5)(4/n)) - (0 + (i - 0.5)(4/n))ยฒ.
Step 5: Write the midpoint Riemann sum in sigma notation. The sum is given by Sโ‚™ = ฮฃแตขโ‚Œโ‚โฟ f(๐“แตข)ฮ”๐“, where ฮ”๐“ = 4/n and f(๐“แตข) is the function value at the midpoint. Substitute ฮ”๐“ and f(๐“แตข) into the formula to express the sum in terms of n and i.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Midpoint Riemann Sum

A Midpoint Riemann Sum is a method for approximating the value of a definite integral. It involves dividing the interval into 'n' subintervals, calculating the midpoint of each subinterval, and then evaluating the function at these midpoints. The sum of these function values, multiplied by the width of the subintervals, provides an estimate of the area under the curve.
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Left, Right, & Midpoint Riemann Sums

Sigma Notation

Sigma notation is a concise way to represent the sum of a sequence of terms. It uses the Greek letter sigma (ฮฃ) to indicate summation, along with an index of summation that specifies the starting and ending values. In the context of Riemann sums, sigma notation is used to express the sum of function values at midpoints across all subintervals.
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Sigma Notation

Definite Integral

A definite integral represents the signed area under a curve defined by a function over a specific interval. It is denoted as โˆซ from 'a' to 'b' of f(x) dx, where 'a' and 'b' are the limits of integration. The definite integral can be approximated using Riemann sums, which provide a numerical method to estimate the area when the exact integral is difficult to compute.
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Related Practice
Textbook Question

Displacement from a velocity graph Consider the velocity function for an object moving along a line (see figure).

(a) Describe the motion of the object over the interval [0,6].

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Textbook Question

{Use of Tech} Approximating definite integrals with a calculator Consider the following definite integrals.

(a) Write the left and right Riemann sums in sigma notation for an arbitrary value of n.


โˆซโ‚€ยน cos โปยน ๐“ d๐“

Textbook Question

Area functions for the same linear function Let ฦ’(t) = 2t โ€• 2 and consider the two area functions A (๐“) = โˆซโ‚หฃ ฦ’(t) dt and F(๐“) = โˆซโ‚„หฃ ฦ’(t) dt .

(a) Evaluate A (2) and A (3). Then use geometry to find an expression for A (๐“) , for ๐“ โ‰ฅ 1 .

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Textbook Question

Properties of integrals Use only the fact that โˆซโ‚€โด 3๐“ (4 โ€•๐“) d๐“ = 32, and the definitions and properties of integrals, to evaluate the following integrals, if possible.

(a) โˆซโ‚„โฐ 3๐“(4 โ€• ๐“) d(๐“)

Textbook Question

Substitutions Suppose ฦ’ is an even function with โˆซโ‚€โธ ฦ’(๐“) d๐“ = 9 . Evaluate each integral.                                                                                                       

(a) โˆซยนโ‚‹โ‚ ๐“ฦ’(๐“ยฒ) d๐“

Textbook Question

Planetary orbits The planets orbit the Sun in elliptical orbits with the Sun at one focus (see Section 12.4 for more on ellipses). The equation of an ellipse whose dimensions are 2a in the ๐“-direction and 2b in the y-direction is (๐“ยฒ/aยฒ) + (yยฒ /bยฒ) = 1.

(a) Let dยฒ denote the square of the distance from a planet to the center of the ellipse at (0, 0). Integrate over the interval [ โ€•a, a] to show that the average value of dยฒ is (aยฒ + 2bยฒ) /3 .